This invention relates generally to an electrophotographic printer or copier, and more particularly concerns a cleaning apparatus used therein.
There are electrophotographic printing machines which use a conductive brush with a negative DC (direct current) bias. Toner charged positively by the preclean dicorotron is thus cleaned by rotating the biased cleaner brush. Detoning of the brush is accomplished with detoning rolls and a flicker bar/vacuum system. This cleaner has difficulty cleaning wrong sign toner and wrong sign paper debris. Blade cleaners are used in many copiers but are not usually used in high volume machines due to their poor reliability. A high toner mass per unit area (M/A) entering the blade cleaner creates a stress input. It has been demonstrated that if the M/A could be reduced, cleaning could be performed at lower minimum blade loads. Additionally, on other machines it has been determined that comet formation (i.e. small deposits, usually consisting of toner and toner additives, which cannot be cleaned from a surface and can grow to a size which creates copy quality defects) on the photoreceptor was reduced by decreasing the blade load, which would be possible if the M/A was reduced. In multicolor copiers and printers of the future, it is important to provide the most robust cleaner designs to assure acceptable cleaning performance over the wide variety of materials and conditions that will be encountered. In an effort to achieve this robust cleaner, some work has been done with a single conductive brush with an AC electrical bias to allow cleaning of both polarity toners with the same brush. This single AC biased brush has been shown to work well on occasion, but frequently redeposition of toner from the brush to the photoreceptor surface (i.e. imaging surface) occurs after the cleaner brush has been used to clean toner from the photoreceptor surface.
Other machines have developed dual brush ESB (electrostatic brush) cleaners, where the first brush is negatively biased and the second brush is positively biased. This type of cleaner is a robust cleaner for two polarities of toner and debris where one brush picks up one polarity and the other brush picks up the opposite polarity. In multicolor copiers and printers of the future, it is important to provide the most robust cleaner designs to assure acceptable cleaning performance over the wide variety of materials and conditions encountered.
The following disclosures may be relevant to various aspects of the present invention and may be briefly summarized as follows:
U.S. Pat. No. 5,256,079 to Lange et al. discloses a cleaning brush electrically biased with an alternating current removes discharged particles from an imaging surface. The particles on the imaging surface are discharged by a corona generating device. A second cleaning device including an insulative brush, a conductive brush or a blade, located upstream of the first mentioned brush, in the direction of movement of the imaging surface, further removes redeposited particles therefrom.
U.S. Pat. No. 4,640,599 to Doutney discloses it has been found that applying an alternating charge to the cleaning brush of a xerographic printer of the reversal development type results in superior neutralization of the residual charge on the photoconductor. This has the advantage of achieving subsequent charging that is uniform.
Xerox Disclosure Journal, Vol. 15, No. 6, Nov./Dec. 1990, pages 463-466, entitled "Dual Electrostatic Brush Cleaner for Cleaning Multiple Toner Types" to Lindblad et al., discloses an improved cleaning arrangement in an electrophotographic device using toner types of different tribocharging characteristics, in which residual toner to be cleaned from a charge retentive surface is charged with a preclean charging arrangement, and removed from the surface with appropriately biased DC electrostatic brush cleaners.